Conventionally, for the phosphor screen of a cathode ray tube (CRT), a field emission type display (FED) and the like, a metal back type structure in which a metal film is formed on the inner surface (surface opposite to a face plate) of a phosphor layer is adopted extensively. In the light emitted from a phosphor by the electrons discharged from an electron source, this metal back layer reflects the light, which advances toward the electron source, to the face plate side to improve luminance and to stabilize the potential of the phosphor layer. It also has a function to prevent the phosphor layer from being damaged by ions which are generated when the gas remaining in a vacuum envelop is ionized.
The metal back layer is conventionally formed by a method (lacquer method) in which a thin film of nitrocellulose is formed on the phosphor layer by a spin method, vacuum deposition of aluminum (Al) is preformed on it, and organic substances is baked and removed.
On the other hand, Japanese Patent Laid-Open Application Sho 63-102139 discloses as a simple method for forming a metal back layer a method (transfer method). In the transfer method, a metal-deposited film is formed on a film on which a parting agent is previously applied and transferred it onto the phosphor layer with an adhesive agent.
The method for forming a metal back layer by the transfer method, however, needs to secure a sufficient adhesive power to the phosphor layer and a baking resistance characteristic in the baking step. But, such characteristics were hardly realized at the same time and the transfer method was conventionally hard to put into actual use.
Specifically, it is necessary to adequately secure an adhesive power by increasing the thickness of the adhesive-agent layer in order to secure a good transfer property, but when the adhesive-agent layer is thick, it is necessary to decompose to scatter a large amount of organic substances in the next baking step. Therefore, the decomposition gas generated at this time causes destruction of the metal film such as a blister, and it is difficult to keep the baking resistance characteristic in good condition.
Japanese Patent Laid-Open Application Hei 3-49131, Japanese Patent Laid-Open Application Hei 4-51423 and Japanese Patent Laid-Open Application Hei 5-190084 disclose a method for remedying a defect resulting from the blister of the metal film in the transfer method by disposing fine pores on the metal film in order to release the decomposition gas. But, such methods had a disadvantage that a side effect was caused to deteriorate the optical reflection performance of the metal back layer.
Japanese Patent Laid-Open Application Sho 64-30134 discloses a structure in which an anchor layer comprising an acryl-based resin or the like is formed between a metal back layer and a parting-agent layer. But, this method is also hard to form a good metal film.
Besides, in the aforementioned lacquer method for forming a metal back layer a metal film is formed on a base surface having large projections and depressions by vacuum deposition, so that it is hard to form a thin film having high reflectance. Therefore, it was hard to obtain a phosphor screen having high luminance, and especially there was a problem of unevenness in luminance on the phosphor screen of the display such as the FED which operates in a low energy electron beam region.
Furthermore, the FED has a gap (space) of about one to several mm between the face plate having the phosphor screen and the rear plate having the electron-emitting element, and the gap cannot be increased in view of resolution and characteristics of a spacer. As a result, a high voltage of about 10 kV is applied to generate a strong electric field in the very small gap between the face plate and the rear plate, resulting in a problem that an electric discharge (dielectrical breakdown) tends to be caused. And, the occurrence of an electric discharge had a tendency of destroying or degrading the electron-emitting element or the phosphor screen.
The present invention has been completed to remedy the above problems, and it is an object of the invention to provide a transfer film capable of forming a metal back layer having good characteristics by a transfer method, a method for forming the metal back layer having remarkable advantageous effects efficiently by the transfer method, and a display device which has a high metal back effect and a remarkable withstand voltage characteristic and can make display with high luminance and high quality.